Aqueous dispersions of polyurethanes or polyurethane ureas have long been known (cf., for example, Angewandete Chemie, 82, (1970) pages 53 to 63; DT-OS Nos. 2,314,512; 2,314,513 or 2,320,719 and U.S. Pat. Nos. 3,920,598, 3,935,146 and 3,905,929) and have a high quality level.
Not least the fact that many of these dispersions are free from emulsifiers contributes towards this high level. They contain chemically incorporated hydrophilic centers which impart self-emulsifiability to the otherwise hydrophobic elastomers. This method of producing self-emulsifiability has two principal advantages over the use of emulsifiers:
(1) less hydrophilic centers are required. PA0 (2) the emulsifier incorporated is unable to migrate from shaped articles produced from elastomer dispersions of this type. As a rule, behavior of this type has a considerable effect upon the property spectrum. PA0 R'--represents a hydrogen atom or a monofunctional hydrocarbon radical having from 1 to 8 carbon atoms, PA0 X--represents a difunctional radical obtained by removing the terminal oxygen atom from a polyalkylene oxide radical having from about 5 to 90 alkylene oxide units of which, based on their number, of which from about 40 to 95% consist of ethylene oxide units and from about 5 to 60% of propylene oxide, butylene oxide or styrene oxide units, PA0 Y--represents oxygen or --NR'''-- and PA0 R" and R''', which may be the same or different, each represent monofunctional hydrocarbon radicals having from 1 to 12 carbon atoms, PA0 Z--represents a radical which has the same definition as Y. PA0 R--represents a difunctional radical of the type obtained by removing the isocyanate groups from a diisocyanate corresponding to the general formula R(NCO).sub.2 of the type mentioned above, PA0 R'--represents a hydrogen atom or a monofunctional hydrocarbon radical having from 1 to 8 carbon atoms, preferably a hydrogen atom or a methyl group, PA0 R"--represents a monofunctional hydrocarbon radical having from 1 to 12 carbon atoms, preferably an unsubstituted alkyl radical having from 1 to 4 carbon atoms, PA0 X--represents a difunctional radical obtained by removing the terminal oxygen atom from a polyalkylene oxide radical having from about 5 to 90 and preferably from about 20 to 70 chain members, of which from about 40 to 95% and preferably from about 60 to 90% consists of ethylene oxide units and from about 5 to 60%, preferably from about 10 to 40%, of propylene oxide, butylene oxide or styrene oxide units, of which propylene oxide units are preferred. PA0 Y--represents oxygen or --NR'''-- wherein R''' has the same definition as R", PA0 X--represents a radical which has the same definition as Y. PA0 (i) corresponding to the following general formula: ##STR5## or (ii) corresponding to the following general formula: ##STR6## wherein R, R", R"', X, Y and Z are as defined above.
The first feature in particular considerably reduces the sensitivity to water of shaped articles produced from self-emulsified polyurethanes. The hydrophilic centers incorporated into known water-dispersible polyurethanes and polyurethane ureas may represent both salt-like, i.e. ionic groups and also hydrophilic non-ionic groups.
The above-mentioned non-ionic, water-dispersible polyurethanes include, in particular, the polyurethanes and polyurethane ureas containing lateral polyethylene oxide chains according to DT-OS Nos. 2,314,512; 2,314,513 and 2,320,719 and U.S. Pat. Nos. 3,920,598, 3,935,146 and 3,905,929.
The non-ionic polyurethane dispersions described in these prior publications are eminently suitable for the production of mechanically strong, highly elastic coatings. Both non-flexible substrates, such as wood and metals, and also flexible substrates, such as textiles or leather may be coated with the dispersions. One preferred field of application is the coating of textiles. However, it has been found that in certain cases, especially in cases where high-gloss transfer papers are used, coated textiles produced using these polyurethanes show a phenomenon which may seriously restrict their commercial value. This phenomenon is the appearance of a coating which becomes increasingly dull in the event of prolonged storage. High-gloss, dark-pigmented or colored coatings in particular show a speckled, matt-grey appearance after from 3 to 6 weeks which seriously affects the optical appearance of the sheet-form material. Although this undesirable phenomenon may be eliminated by wiping with a damp cloth, it reappears after a certain time.
Accordingly, an object of the present invention is to provide non-ionic, water-dispersible polyurethanes which may be used for the production of textile coatings which do not show the unfavorable phenomenon referred to above. According to the present invention, this object may surprisingly be achieved by incorporating certain quantities of other alkylene oxide units in addition to ethylene oxide units into the polyether side chains which are responsible for the dispersibility of the polyurethanes.